1. Field of the Invention
The present invention relates to a wafer holder which is capable of handling semiconductor wafers (hereafter referred simply to as wafers) of any of selected different diameters and an apparatus for vapor-drying wafers using the wafer holder.
2. Description of the Prior Art
In semiconductor device fabrication processes, impurities and foreign matter adhered on the surface of a wafer have an adverse influence on the performance of semiconductor devices therefrom.
A cleaning operation is therefore indispensable in processes for producing wafers. And there are available a variety of cleaning methods in the cleaning operation for a process for producing wafers, which are most broadly classified into the two groups of physical methods and chemical methods.
In the physical methods, included are a method in which impurities stuck on the surface of a wafer are directly removed by the mechanical action of a washing brush, another method in which a pressurized liquid is shot in a stream onto part or all of the surface of a wafer from a jet nozzle and thereby the impurities are removed and still another method in which impurities stuck on the surface of a wafer are removed by application of ultrasonic waves (which is a so-called ultrasonic cleaning method).
In the chemical methods, impurities stuck on the surface of a wafer are chemically decomposed into constituents to be removed by the powers of chemicals or enzymes. Mechanical and chemical methods may be combined so as to improve the total cleaning capacity.
In the practical application of the above-mentioned cleaning methods, two types of transportaion of wafers are known for feeding them into the cleaning means, in one of which a plurality of wafers are accommodated in a carrier cassette made from plastics for transportation (carrier type) and in the other of which a wafer(s) is grasped by a robot hand and so on for transportation (carrier-less type).
A cleaning apparatus of the carrier type has a demerit that wafers are by chance polluted by adhesion of particles or the like, which may be generated by friction between some of the wafers and the carrier cassette, but has a merit that wafers of different diameters are easier to handle in the same cleaning apparatus by exchange of carrier cassettes in dependence on a selected diameter thereof.
While the cleaning apparatus of the carrier-less type does not have a demerit of wafer-pollution caused by a carrier cassette, but has a great difficulty of constraint originating from the structures themselves of both a wafer holder used within a cleaning bath and a robot hand for transportation of wafers.
In a drying apparatus corresponding to the above-mentioned cleaning apparatus of the carrier-less type, it is also necessary for a similar reason to the great difficulty from the structures that when the same drying apparatus handles wafers of different diameters a wafer holder and/or a robot hand for transportation of wafers are exchanged in dependence on selected diameters thereof or in another case a cleaning device and drying device are selected to match the respective diameters and thus the efficiency of operation thereof is reduced to a great extent.